Detecting the health of an inkjet nozzle has been a long standing problem in the field. With scanning printheads the ability to perform multiple passes has been used to minimize the impact of missing or improperly performing nozzles. As inkjet technology pushes into the laser printer performance space, printheads with nozzles spanning the entire page width have become more common. Using this printing method yields improved print speeds but no longer allows for multi-pass printing. Therefore, a method to verify that a nozzle is jetting properly is needed.
One such method is by optical detection as disclosed in U.S. Pat. Nos. 8,177,318, 8,376,506 and 8,449,068, as well as others. This method requires external light sources and sensors which can add cost and complexity to the printing device. In an effort to eliminate the need for external devices, other methods have been disclosed which place impedance sensors on the ejector chip itself.
One possible implementation of this method is described in U.S. Pat. Nos. 8,870,322 and 8.899,709 and US Patent Application Publication 2014/0333694. These patents and application teach the use of either differential or single ended impedance measurements taken over time to detect the formation and collapse of thermal vapor bubbles. It is further taught that different types of nozzle conditions such as blocked or weak nozzles can be determined by external processing of the data collected from the sensors. As shown in U.S. Pat. No. 8,870,322, a method of calibration may be required to provide adequate performance of the system. These conventional techniques of detecting printhead condition require analysis of each sensor output at each ink chamber to determine whether the nozzle corresponding to that chamber is firing properly. This does not allow for a practical and efficient detection method.